71. A solid iron pole consists of cylinder of height 220cm and base diameter 24cm, which is surmounted by another cylinder of height 60cm and radius 8cm. find the mass of the pole, given that 1cm3 of iron has approximately 8g mass. (Use =3.14).(892.26)
72. The height of a cone is 30 cm. A small cone is cut off at the top by a plane parallel to the base. If its volume be of the volume of the given cone, at what height above the base, the section has been made? (20)
73. If the nth terms of an A.P is (2n + 1), find the sum of first n terms of the A.P.
74. Find the sum of first 10 terms of an A.P., in which 3rd term is 7 and 7th term is two more than thrice of its 3rd term.
75. If the sum of n terms of an A.P.is same as the sum of its n terms, show that the sum of its (m + n) terms is zero.
76. Find the sum of first n odd natural numbers.
77. If the 8th terms of an A.P.is 31 and the 15th terms is 16 more than the 11th terms find the sum of first 20 terms.
78. How many terms of A.P.: 24,21,18,…….. Must be taken so that their sum is 78?
79. The angles of a triangle are in AP.If the greatest angle equals the sum of the other two, find the angles.
80. How many terms of the sequence 18,16,14…… should be taken so that their sum is zero.
72. The height of a cone is 30 cm. A small cone is cut off at the top by a plane parallel to the base. If its volume be of the volume of the given cone, at what height above the base, the section has been made? (20)
73. If the nth terms of an A.P is (2n + 1), find the sum of first n terms of the A.P.
74. Find the sum of first 10 terms of an A.P., in which 3rd term is 7 and 7th term is two more than thrice of its 3rd term.
75. If the sum of n terms of an A.P.is same as the sum of its n terms, show that the sum of its (m + n) terms is zero.
76. Find the sum of first n odd natural numbers.
77. If the 8th terms of an A.P.is 31 and the 15th terms is 16 more than the 11th terms find the sum of first 20 terms.
78. How many terms of A.P.: 24,21,18,…….. Must be taken so that their sum is 78?
79. The angles of a triangle are in AP.If the greatest angle equals the sum of the other two, find the angles.
80. How many terms of the sequence 18,16,14…… should be taken so that their sum is zero.
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